I've looked at https://gcc.gnu.org/wiki/FloatingPointMath
and there may be some mistakes or missing info. First, it is said that x / C is replaced by x * (1.0 / C) when C is a power of two. But this condition is not sufficient: if 1.0 / C overflows, the transformation is incorrect. From some testing, it seems that GCC detects the overflow case, so that it behaves correctly. In this case I think that the wiki should say: "When C is a power of two and 1.0 / C doesn't overflow." It is also said that x / 1.0 and x / -1.0 are respectively replaced by x and -x. But what about x * 1.0 and x * -1.0? Ditto with -(a / b) -> a / -b and -(a / b) -> -a / b. Is there anything similar with multiplication? -- Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
